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Friday, April 5, 2019

V-speed Designator Description





V is for Speed
The “V” is from the French word ‘Vitesse’ which means ‘speed’ or ‘rate’. Important aviation Airspeeds are identified and defined using standard terms. Scientists and Engineers refer to Airspeeds as ‘V’ Speeds. Commonly, people think in terms of “Velocity”, and it is a nice memory aid, as “Velocity” begins with “V”. But, technically “Velocity” is defined as “Speed in a particular direction”. So, as a memory aid, you may loosely think of “V-Speeds” as “Velocity Speeds”, but to be more accurate, the ‘V’ is for ‘Vitesse’. V-Speeds are Airspeeds defined for specific maneuvers in specific aircraft at specific configurations.
Aircraft designers and manufacturers perform flight tests to help determine performance limitations of aircraft. The resulting flight test data is used to help determine specific best practice speeds for safe operation of the aircraft. Recommended Airspeeds (V-Speeds) are published and these airspeeds are relied on for best performance and safety of the aircraft. Pilots should be knowledgeable about the published V-Speeds for each type and configuration of aircraft they fly.
V1
Engine failure recognition speed or decision speed. It is the maximum speed in the take-off
at which the pilot must take the first action (e.g., apply brakes, reduce thrust, deploy speed
brakes) to stop the airplane within the accelerate-stop distance. V1 also means the
minimum speed in the take-off, following a failure of the critical engine at VEF, at which the
pilot can continue the take-off and achieve the required height above the take-off surface
within the take-off distance. If an engine failure is detected after V1, the take-off must be
continued. This implies that the aircraft must be controllable on ground. Therefore, V1 is
always greater than VMCG.
V2
Take-off safety speed. It is the minimum speed that needs to be maintained up to
acceleration altitude, in the event of an engine failure after V1. Flight at V2 ensures that the
minimum required climb gradient is achieved, and that the aircraft is controllable.
V2 speed is always greater than VMCA, and facilitates control of the aircraft in flight.
In an all-engines operative take-off, V2+10 provides a better climb performance than V2.
V3 
Flap retraction speed.
V4
Steady initial climb speed. The all engines operating take-off climb speed used to the point
where acceleration to flap retraction speed is initiated. Should be attained by a gross
height of 400 feet.
VA
Design manoeuvring speed. This is the speed above which it is unwise to make full
application of any single flight control (or "pull to the stops") as it may generate a force
greater than the aircraft's structural limitations.
Vat
Indicated airspeed at threshold, which is equal to the stall speed VS0multiplied by 1.3 or
stall speed VS1g multiplied by 1.23 in the landing configuration at the maximum certificated
landing mass. If both VS0 and VS1g are available, the higher resulting Vat shall be applied.
Also called "approach speed".
VB 
Design speed for maximum gust intensity.
VC Design cruise speed, used to show compliance with gust intensity loading.
Vcef generally used in documentation of military aircraft performance as V1
VD Design diving speed.
VDF Demonstrated flight diving speed.
VEF The speed at which the Critical engine is assumed to fail during take-off.
VFDesigned flap speed.
VFC 
Maximum speed for stability characteristics.
VFE 
Maximum flap extended speed.
VFTO
Final take-off speed
VH 
Maximum speed in level flight at maximum continuous power.
VLE
Maximum landing gear extended speed. This is the maximum speed at which it is safe to fly
a retractable gear aircraft with the landing gear extended.
VLO
Maximum landing gear operating speed. This is the maximum speed at which it is safe to
extend or retract the landing gear on a retractable gear aircraft.
VLOF Lift-off speed.
VMC
Minimum control speed. Mostly used as the minimum control speed for the take-off
configuration (take-off flaps) in many publications. Several VMC's exist for different flight
phases and airplane configurations: VMCG, VMCA, VMCA1, VMCA2, VMCL, VMCL1, VMCL2. Refer to the
minimum control speed article for a thorough explanation.
VMCA
Minimum control speed in the air (or airborne) for maintaining steady straight flight when
an engine fails or is inoperative and with the corresponding opposite engine set to provide
maximum thrust, provided a small (3° – ) 5° bank angle is being maintained away from the
inoperative engine and the rudder is used up to maximum to maintain straight flight. The
exact required bank angle should be provided by the manufacturer with VMC(A) data. Refer
to the minimum control speed article for a description of (pilot-induced) factors that have
influence on VMCA. VMCA is also presented as VMC in many manuals.
VMCG
Minimum control speed on the ground is the lowest speed at which the take-off may be
safely continued following an engine failure during the take-off run. Below VMCG, the throttles need to be closed at once when an engine fails, to avoid veering off the runway.
VMCL Minimum control speed in the landing configuration with one engine inoperative.
VMO Maximum operating limit speed.
VMU
Minimum unstick speed. It is achieved by pitching the aircraft up to the maximum (tail on
the runway, for aircraft that are geometrically-limited) during the take-off roll. The speed
at which the aircraft first lifts off is VMU. Therefore, lift-off is not possible prior to VMU.
VNE Never exceed speed.
VNO Maximum structural cruising speed or maximum speed for normal operations.
VO Maximum operating manoeuvring speed.
VR
Rotation speed. The speed at which the aircraft's nose wheel leaves the ground during
take-off.
Vrot
Used instead of VR (in discussions of the take-off performance of military aircraft) to
denote rotation speed in conjunction with the term VRef (refusal speed).
VRef
Landing reference speed or threshold crossing speed.
VRef stands for refusal speed for military aircraft. Refusal speed is the maximum speed during take-off from which the air vehicle can stop within the available remaining runway
length for a specified altitude, weight, and configuration.
VS 
Stall speed or minimum steady flight speed for which the aircraft is still controllable.
VS0 
Stall speed or minimum flight speed in landing configuration.
VS1
Stall speed or minimum steady flight speed for which the aircraft is still controllable in a
specific configuration.
VSR 
Reference stall speed.
Prepared by : Air.Net Team

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